How about allow freeform but the freeform type character will be treated differently than the regular archetype character. Freeform can choose powers from different power sets and have relatively better stats than the regular character. However the freeform character in terms of PvP is relegated a specific role. For example, there is a PvP zone where the freeform character fights against 5 regular characters and/or a PvP zone only where freeform characters duke it out.

There could be a PvP zone where each side has 1 freeform character join to complete an objective while there are 5 other regular characters on his side accomplishing a different objective.

In order to make a freeform character you must do any of these things.

1. Buy LTS (Lifetime Subscription) and you can make as much freeform characters as you want.
2. Buy a freeform character slot if you're not LTS.
3. Earn a freeform character slot from a special event.